This is perhaps the strongest of the several "I am" statements in this part of the book (see Theological Themes). God says personally and directly who God is, making clear that there is no other God.
This text can be comforting and disturbing. The other gods, who mean Israel ill, are dismissed, leaving only the Lord, the God of the exodus, as the divine power in the life of Israel and the world--good news, indeed! But power is seen both in light and darkness, both in weal and in woe. What does it mean that God is Lord of both? Is this still good news, especially if one translates with KJV: "I make peace, and create evil"?
Isaiah's primary point remains always good news--there is no other divine power. The ancient gods might well be good or evil spirits, lords of light or lords of darkness. But Israel's God is One, God alone, and Israel's God is always the God of steadfast love. All aspects of life, the good and the bad, are finally in the hands of a loving God.
The text does not imply that everything that happens is God's will. Isaiah recognizes that Israel acts contrary to God's will (for example, 43:27-28) and so do the nations (47:6-7). In this book there are many agents who have real power to do good or ill: Israel, the servant, the prophet, Cyrus, Babylon, the nations, and others. But there is only one God, only one who has power in heaven.
This passage ascribes the "darkness" and "woe" that Israel has experienced in its exile to God; it does not mean to say the power of "Evil" itself is God's creation. To be sure, Israel has brought darkness upon itself by its own sin, but ultimately God has taken charge of that darkness to turn Israel from sin to renewal (40:2).
5 I am the Lord, and there is no other;
besides me there is no god.
I arm you, though you do not know me,
6 so that they may know, from the rising of the sun
and from the west, that there is no one besides me;
I am the Lord, and there is no other.
7 I form light and create darkness,
I make weal and create woe;
I the Lord do all these things.
New Revised Standard Version Bible: Anglicized Edition, copyright © 1989, 1995 National Council of the Churches of Christ in the United States of America. Used by permission. All rights reserved worldwide. http://nrsvbibles.org